Re: [PATCH v8 2/2] drm/i915: Allow "max bpc" property to limit pipe_bpp

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 18, 2018 at 11:11:15AM -0700, Radhakrishna Sripada wrote:
> Use the newly added "max bpc" connector property to limit pipe bpp.
> 
> V3: Use drm_connector_state to access the "max bpc" property
> V4: Initialize the drm property, add suuport to DP(Ville)
> V5: Use the property in the connector and fix CI failure(Ville)
> V6: Use the core function to attach max_bpc property, remove the redundant
>     clamping of pipe bpp based on connector info
> V7: Fix Checkpatch warnings
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Kishore Kadiyala <kishore.kadiyala@intel.com>
> Cc: Manasi Navare <manasi.d.navare@intel.com>
> Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> Signed-off-by: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 49 ++++++++++++++++++++----------------
>  drivers/gpu/drm/i915/intel_dp.c      |  5 ++++
>  drivers/gpu/drm/i915/intel_hdmi.c    |  5 ++++
>  3 files changed, 38 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index eb25037d7b38..75afd53590b1 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10845,29 +10845,37 @@ static void intel_modeset_update_connector_atomic_state(struct drm_device *dev)
>  }
>  
>  static void
> -connected_sink_compute_bpp(struct intel_connector *connector,
> -			   struct intel_crtc_state *pipe_config)
> +connected_sink_max_bpp(struct drm_connector_state *conn_state,
> +		       struct intel_crtc_state *pipe_config)
>  {
> -	const struct drm_display_info *info = &connector->base.display_info;
> -	int bpp = pipe_config->pipe_bpp;
> -
> -	DRM_DEBUG_KMS("[CONNECTOR:%d:%s] checking for sink bpp constrains\n",
> -		      connector->base.base.id,
> -		      connector->base.name);
> -
> -	/* Don't use an invalid EDID bpc value */
> -	if (info->bpc != 0 && info->bpc * 3 < bpp) {
> -		DRM_DEBUG_KMS("clamping display bpp (was %d) to EDID reported max of %d\n",
> -			      bpp, info->bpc * 3);
> -		pipe_config->pipe_bpp = info->bpc * 3;
> +	if (pipe_config->pipe_bpp < conn_state->max_bpc * 3) {
> +		conn_state->max_bpc = pipe_config->pipe_bpp / 3;
> +		return;

This back and forth between max_bpc and pipe_bpp is a bit confusing.
I'd probably leave max_bpc alone here and just update pipe_bpp as
needed.

>  	}
>  
> -	/* Clamp bpp to 8 on screens without EDID 1.4 */
> -	if (info->bpc == 0 && bpp > 24) {
> -		DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of 24\n",
> -			      bpp);
> -		pipe_config->pipe_bpp = 24;
> +	switch (conn_state->max_bpc) {

This is missing the 6bpc case at least. I suppose the current code
isn't particuraly robust against unexpected values coming via
info->bpc. The switch statement does seem an improvement in that
regard. Though would be nice to compact it a bit using eg. the gcc 
case range extension.

> +	case 8:
> +	case 9:
> +		pipe_config->pipe_bpp = 8 * 3;
> +		break;
> +	case 10:
> +	case 11:
> +		pipe_config->pipe_bpp = 10 * 3;
> +		break;
> +	case 12:
> +	case 13:
> +	case 14:
> +	case 15:

With the proposed min() we'd never get bpc > 12 here.

> +		pipe_config->pipe_bpp = 12 * 3;
> +		break;
> +	case 16:
> +		pipe_config->pipe_bpp = 16 * 3;
> +		break;
> +	default:
> +		break;

Maybe just return an error here. I suppose it should never happen unless
there's some bogus displays out there that report < 6 bpc.

>  	}
> +
> +	DRM_DEBUG_KMS("Limiting display bpp to %d\n", pipe_config->pipe_bpp);

Would be nice to include all the relevant information in this debug
print: original pipe_bpp, info->bpc*3, max_requested_bpc.

Maybe something like this would work to keep the code easy to read:
{
	bpp = min(pipe_bpp, max_bpc*3);

	switch (bpp) {
	...
	}

	if (bpp != pipe_bpp) {
		DRM_DEBUG_KMS(...);
		pipe_bpp = bpp;
	}
}

>  }
>  
>  static int
> @@ -10898,8 +10906,7 @@ compute_baseline_pipe_bpp(struct intel_crtc *crtc,
>  		if (connector_state->crtc != &crtc->base)
>  			continue;
>  
> -		connected_sink_compute_bpp(to_intel_connector(connector),
> -					   pipe_config);
> +		connected_sink_max_bpp(connector_state, pipe_config);
>  	}
>  
>  	return bpp;
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 436c22de33b6..aefca1d9e87b 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -5719,6 +5719,11 @@ intel_dp_add_properties(struct intel_dp *intel_dp, struct drm_connector *connect
>  		intel_attach_force_audio_property(connector);
>  
>  	intel_attach_broadcast_rgb_property(connector);
> +	if ((IS_G4X(dev_priv) || IS_VALLEYVIEW(dev_priv) ||
> +	     IS_CHERRYVIEW(dev_priv)))

Just HAS_GMCH_DISPLAY() will do here.

> +		drm_connector_attach_max_bpc_property(connector, 8, 10);
> +	else if (INTEL_GEN(dev_priv) >= 5)
> +		drm_connector_attach_max_bpc_property(connector, 8, 12);

DP does support 6 bpc as well, so we may want to reduce the min to 6
here.

>  
>  	if (intel_dp_is_edp(intel_dp)) {
>  		u32 allowed_scalers;
> diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
> index a2dab0b6bde6..2b432c7e4f8a 100644
> --- a/drivers/gpu/drm/i915/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> @@ -2109,11 +2109,16 @@ static const struct drm_encoder_funcs intel_hdmi_enc_funcs = {
>  static void
>  intel_hdmi_add_properties(struct intel_hdmi *intel_hdmi, struct drm_connector *connector)
>  {
> +	struct drm_i915_private *dev_priv = to_i915(connector->dev);
> +
>  	intel_attach_force_audio_property(connector);
>  	intel_attach_broadcast_rgb_property(connector);
>  	intel_attach_aspect_ratio_property(connector);
>  	drm_connector_attach_content_type_property(connector);
>  	connector->state->picture_aspect_ratio = HDMI_PICTURE_ASPECT_NONE;
> +
> +	if (!HAS_GMCH_DISPLAY(dev_priv))
> +		drm_connector_attach_max_bpc_property(connector, 8, 12);
>  }
>  
>  /*
> -- 
> 2.9.3

-- 
Ville Syrjälä
Intel
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